Because of their unique sieving characteristics as well as their catalytic properties, crystalline molecular sieves and zeolites are especially useful in applications such as hydrocarbon conversion, gas drying and separation.
Recently, Zones et al. reported the preparation of multidimensional 10-ring channel system SSZ-74, and its use in various hydrocarbon conversion and separation processes (see WO 2007/079038; U.S. Pat. No. 7,422,732; U.S. Pat. No. 7,357,904; U.S. Pat. No. 7,348,295; US 2007/0144939; US 2007/0148067; US 2007/0148086; US 2007/0149778; US 2007/0149789; US 2007/0149824; US 2007/0149837; and, Baerlocher et al. “Ordered silicon vacancies in the framework structure of the zeolite catalyst SSZ-74”, Nature Materials, 2008 August; 7(8):631-5). SSZ-74 is a 3-dimensional medium pore zeolite with a silicon vacancy. Up to now, the method of preparing SSZ-74 has comprised contacting under crystallization conditions (1) a source of silicon oxide, (2) a source of aluminum oxide, indium oxide and mixtures thereof, (3) fluoride ions and (4) a structure directing agent comprising a 1,1′-(hexane-1,6-diyl)bis(1-methylpyrrolidinium) dication having the following structure 1,1′-(hexane-1,6-diyl)bis(1-methylpyrrolidinium)

Although effective in producing the SSZ-74 crystal structure, the method requires the use of a source of fluoride ions posing potential safety and health concerns during manufacture. The use of fluoride in zeolite reaction gels is undesirable on a large scale because of the potential hazards involved. Anhydrous or aqueous hydrogen fluoride can cause painful and severe burns and even death.
There thus remains a need for a method of synthesizing a synthetic crystalline material that eliminates the need for a source of fluoride yet maintains a high purity yield of the material.
The present invention provides such a method. Specifically, the present invention provides a method of preparing a synthetic crystalline material having an SSZ-74 crystal structure in the absence of a source of fluoride ions.